Many heated water tubs and pools for bathers and swimmers are located out of doors. When they are not being used, covers are placed over the water surface to keep as much heat as possible below the cover. When these covers are made firm enough to be lifted off in one piece or in several pieces, or to be tilted off to one side, they are preferably made to be watertight, so their respective overall weight will not be increased by rain water entering and staying within the cover.
However, many covers originally designed and made to be watertight, may at the outset have material imperfections, and/or manufacturing defects which are not easily detectable, and therefore they may become filled in part or completely with rain water. Or covers may at the outset of their installation, or at a later time, because of often unknown causes, such as accidental punctures or blows to the cover, etc., become altered enough so rain water or condensed water collects within the cover.
Although manufacturers and users of these covers would initially prefer that no drain holes be made or provided for in these covers, they realize that a well positioned drain is, in a practical way, a necessity. Yet when an intended and designed drain is provided in a cover, then hot vapors are known to raise and to enter the intended drain and thereafter condense within a cover and remain for a while. When this occurs, the potential exists for the water held within the cover to vaporize and enter the cells of the insulating core of the cover. Then these vapors within these cells condense, and this condensed water becomes locked in these cells of the insulating core, thereby causing the unwanted process of saturation and weight gain of the cover.